Acute rejection remains a vexing problem in renal transplantation: it is the most common cause of transplant failure and its therapy results in significant adverse events. Humanized anti-TAC (HAT) is a new monoclonal antibody which has been shown in a pilot trial to be effective in preventing acute rejection with minimal side effects. In this multicenter trial, 260 patients at 20 transplant centers in the US and Canada will be randomized to receive either standard three-drug immunosuppressive therapy (cyclosporine, azathioprine, prednisone) or the same drugs along with HAT to prevent rejection during the first 90 days following transplant. HAT has unique characteristics which allow it to be administered every 14 days. The first dose is given during the transplant operation. Doses 2-5 (at 2, 4, 6, and 8 weeks posttransplant) require outpatient assessment and administration. These visits occur in the GCRC, where each patient undergoes a physical exam, laboratory evaluation of allograft function, insertion of an intravenous catheter, and administration of study drug in a controlled environment. The endpoint of this blinded trial is frequency of acute rejection within the first six months following transplant. At the current time, the study remains blinded, with no results available. So far, twenty-one patients have been enrolled at UAB.